Amplifying a signal using a current shared power amplifier

ABSTRACT

A power amplifier includes amplifier stages. An amplifier stage includes a transistor, and at least one amplifier stage comprises a driver stage. The amplifier stages include a first amplifier stage having a first transistor and associated with a first output power, and a second amplifier stage having a second transistor and associated with a second output power. A current sharing coupling couples the first amplifier stage and the second amplifier stage. The first amplifier stage and the second amplifier stage share a current through the current sharing coupling. The current sharing coupling facilitates scaling of the first output power and the second output power.

GOVERNMENT FUNDING

The U.S. Government may have certain rights in this invention asprovided for by the terms of Contract No. (classified) awarded by(classified).

TECHNICAL FIELD

This invention relates generally to the field of power amplifiers andmore specifically to amplifying a signal using a current shared poweramplifier.

BACKGROUND

A power amplifier includes driver stages, where each driver stagesupplies excitation to a next driver stage. Each driver stage consumespower to operate. The power consumed by the driver stages, however,reduces the power added efficiency of the power amplifier.

There are known techniques for improving the power added efficiency of apower amplifier. According to one known technique, the bias point,output matching network, or harmonic terminations of a power amplifiermay be adjusted to decrease the DC power of the output stage of theamplifier. Decreasing the output stage DC power by matching to anefficiency load target may increase power added efficiency. According toanother technique, the size of the driver stages may be reduced tominimize the power consumed by the driver stages. Minimizing powerconsumption by the driver stages may increase power added efficiency.Reducing the drive stage size, however, may not work for low outputpower amplifiers. The input stage for a low output power amplifier maybe required to be extremely small, and extremely small stages aredifficult to match.

SUMMARY OF THE DISCLOSURE

In accordance with the present invention, disadvantages and problemsassociated with previous techniques for amplifying a signal may bereduced or eliminated.

According to one embodiment of the present invention, a power amplifierincludes amplifier stages. An amplifier stage includes a transistor, andat least one amplifier stage comprises a driver stage. The amplifierstages include a first amplifier stage having a first transistor andassociated with a first output power, and a second amplifier stagehaving a second transistor and associated with a second output power. Acurrent sharing coupling couples the first amplifier stage and thesecond amplifier stage. The first amplifier stage and the secondamplifier stage share a current through the current sharing coupling.The current sharing coupling facilitates scaling of the first outputpower and the second output power.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that currentmay be shared between driver stages of a power amplifier. The outputpower of each stage may be scaled to control power consumption by thedriver stages. The output power scaling may improve the power addedefficiency of the power amplifier.

Certain embodiments of the invention may include none, some, or all ofthe above technical advantages. One or more other technical advantagesmay be readily apparent to one skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a circuit diagram of one embodiment of a power amplifier thatmay be used to amplify a signal;

FIG. 2 is a circuit diagram of an example power amplifier of theembodiment of FIG. 1; and

FIG. 3 is a graph illustrating the driver performance over voltage of anexample power amplifier of the embodiment of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1 through 3 of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1 is a circuit diagram of one embodiment of a power amplifier 10that may be used to amplify a signal. In general, current may be sharedbetween the driver stages of amplifier 10. The output power of eachstage may be scaled to control power consumption by the driver stages.The output power scaling may improve the power added efficiency of thepower amplifier.

According to the illustrated embodiment, amplifier 10 is coupled tointegrated circuits 20 as shown. Amplifier 10 may receive a signal,amplify the signal, and transmit the amplified signal. An integratedcircuit may refer to a circuit comprising a semiconductor material, forexample, silicon. The components and connections of the circuit may beformed by processing areas of the semiconductor material. Amplifier 10,however, may be coupled to any suitable circuits. For example, amplifier10 may be coupled to hybrid circuits. The semiconductor active devicemay be placed on a secondary material used to route bias and providematching.

Amplifier 10 includes a resistor 30, terminals 34, and stages 38 coupledas shown. Amplifier 10 amplifies a received signal, and may have anysuitable power amplifier gain. For example, amplifier 10 may have apower amplifier gain of less than 40 decibels, such as less than 30 or20 decibels. Amplifier 10 may have any suitable input power and outputpower. For example, amplifier 10 may have an input power ofapproximately −30 dBm to +15 dBm, an output power of approximately 0 dBmto +30 dBm.

Voltages may be applied to terminals 34. A terminal may refer to a pointof a device at which a voltage is applied. A gate voltage V_(g) may beapplied to terminal 34 b, and a drain voltage V_(d) may be applied toterminal 34 a. Gate voltage V_(g) may be approximately −0.1 to −0.7volts (V), such as approximately −0.5 V, and drain voltage V_(d) may beapproximately 2 to 8 V, such as approximately 7 V.

A stage may refer to a stage of an amplifier that processes a signal.Examples of stages include driver stages and output stages. A driverstage 38 supplies excitation to a next driver stage 38. A driver stagemay refer to an amplifier stage that supplies excitation, such ascurrent, power, or voltage excitation, to a next stage, and may includea field effect transistor and matching circuits made of tuning elementssuch as lines, resistors, and capacitors between the transistors.According to the illustrated embodiment, driver stage 38 a suppliesexcitation to driver stage 38 b, and driver stage 38 b providesexcitation to driver stage 38 c. Each stage 38 may have any suitablegain to yield any suitable power amplifier gain. For example, atmicrowave frequencies, a stage 38 may have a gain of approximately 10decibels (dB) to yield a power amplifier gain of approximately 30 dB.

A driver stage 38 includes, at a minimum, a capacitor 42 and atransistor 46. A capacitor may refer to a passive electronic circuitcomponent comprising metal electrodes separated by a dielectric.Capacitors 42 may have any suitable capacitance. For example, capacitor42 a may have the capacitance of approximately 0.1 to 10 picoFarads(pF), such as approximately 1.5 pF. Capacitor 42 b may have acapacitance of approximately 0.1 to 10 pF, such as approximately 7 pF.Capacitor 42 c may have a capacitance of approximately 0.1 to 10 pF,such as approximately 3 pF.

A transistor may refer to a semiconductor device that amplifies asignal. Transistor 46 may comprise any suitable transistor. According toone embodiment, transistor 46 a may be approximately the same size astransistor 46 b. For example, transistors 46 a and 46 b may beapproximately 30 to 250 micrometers (μm), such as approximately 200 μm.

Transistors 46 a and 46 b may have other suitably similar features. Thedrain-source voltages V_(DS) of transistors 46 a and 46 b may beapproximately 1 to 6 V. For example, transistor 46 a may have adrain-source voltage V_(DS) of approximately 3.1 V, and transistor 46 bmay have a drain-source voltage V_(DS) of approximately 3.9 V. The peakcurrents I_(P) of transistors 46 a and 46 b may be approximately 35 to40 milliamps (mA). For example, the peak currents I_(P) may beapproximately 38 mA.

Transistors 46 a and 46 b may also have any suitable load-targetresistance (R_(P)), based on the transistor size, applied voltage, andpower required to drive following amplifier stages. For example,transistor 46 a may have a resistance R_(P) of approximately 5 to 40ohms-millimeters (Ω-mm), such as approximately 8 Ω-mm, and transistor 46b may have a resistance of approximately 5 to 40 Ω-mm, such asapproximately 18 Ω-mm. Based on the load-target and the applied voltage,the power output P_(out) of transistors 46 a and 46 b may beapproximately −20 to 25 dBm (decibels relative to one milliwatt). Forexample, transistor 46 a may have an output power capacity ofapproximately 10 dBm, and transistor 46 b may have an output powercapacity of approximately 18 dBm. The DC power consumed by transistors46 a and 46 b is calculated from the total voltage V_(d) across thetransistors and the equal-current flowing through the transistors. Thevalues may be, for example, 7 V and 15 mA, with a corresponding DC powerconsumption of 105 mW. The DC power consumption may be less than 15percent of the power capability of the output device.

Transistor 46 c may be larger than transistors 46 a and 46 b. Accordingto one embodiment, transistor 46 c may be approximately 400 to 600 μm,for example, approximately 450 or 550 μm. Transistor 46 c may have adrain-source voltage V_(DS) of approximately 3 to 10 V, such asapproximately 7 V. The peak current I_(P) may be approximately 70 to1000 mA, such as approximately 78 mA. The load-target resistance R_(P)may be approximately 30 to 40 Ω-mm, such as approximately 38 Ω-mm. Theoutput power may be approximately 20 to 30 dBm, such as approximately 25dBm. The DC power may be approximately 500 to 2000 mW, such asapproximately 1000 mW.

Resistors 30 and 50 may be used to set the gate voltage on driver stage38 a. When current sharing, the gate voltage of first driver stage 38 ais positive and may be used to adjust the voltage split. For example, ifthe nominal gate-to-source voltage for operating the transistor is −0.4V, then to place ⅓ of the voltage on driver stage 38 a, the voltage setby resistors 30 and 50 is V_(d)/3−0.4 V.

According to one embodiment, stages 38 of amplifier 10 may share acurrent. For example, stage 38 a and 38 b may share a current through acurrent sharing coupling 52. Current sharing coupling 52 may compriseany suitable connection operable to conduct current. The current sharingyields a substantially equivalent current between stages 38 a and 38 b.The current sharing may allow for the driver stages sharing the currentto have transistors of approximately the same size. For example,transistor 46 a may be approximately the same size as transistor 46 b.

The power added efficiency (PAE) of amplifier 10 may be definedaccording to the following equation:

$\begin{matrix}{{PAE} = \frac{P_{out} - P_{i\; n}}{{D\; C_{os}} + {D\; C_{ds}}}} & (1)\end{matrix}$where P_(out) represents the output power of amplifier 10, P_(in)represents the input power of amplifier 10, DC_(os) represents thedirect current (DC) power of the output stage, and DC_(ds) representsthe DC power of driver stages 38. Accordingly, an increase of the DCpower DC_(ds) of the driver stages 38 decreases the power addedefficiency.

According to one embodiment, the DC power DC_(ds) of driver stages 38may be reduced by adjusting the size of the transistors and the voltageratio between stages 38. A voltage ratio between a first stage and asecond stage may refer to a ratio of the power applied to a firsttransistor of the first stage to the power applied a second transistorof the second stage. According to the embodiment, a lower voltage may beapplied at stages 38 a and 38 b then at stage 38 c. Gate voltages may beadjusted to set the voltage ratio to obtain a desired ratio betweenstages 38 a and 38 b and stage 38 c in order to reduce the DC power ofdriver stages 38. The desired ratio may be approximately two-to-one, butmay be as high as five-to-one. For example, voltage applied at stages 38a and 38 b may be approximately 2 to 4 V, such as approximately 3.1 Vfor stage 38 a and approximately 3.9 V for stage 38 b. The voltageapplied at stage 38 c may be approximately 6 to 8 V volts, such asapproximately 7.0 V.

Stage 38 b may be operated under compression to allow for optimizingpower added efficiency. According to one embodiment, the current sharingmay be reversed to allow stage 38 b to set the current, which may allowthe current to increase under compression.

In operation, power amplifier 10 receives a signal. Driver stage 38 aapplies excitation to the received signal, which travels to driver stage38 b. Driver stage 38 b applies excitation to the signal. Current may beshared between driver stages 38 a and 38 b. The output power of driverstages 38 a and 38 b may be scaled to control power consumption. Theoutput power may be scaled by scaling the voltage, transistor size,resistance, or any combination of the preceding at each stage 38. Theoutput power scaling may improve the power added efficiency of poweramplifier 10. Driver stage 38 c applies excitation to the signal andoutputs the amplified signal.

Modifications, additions, or omissions may be made to amplifier 10without departing from the scope of the invention. The components ofamplifier 10 may be integrated or separated according to particularneeds. Moreover, the operations of amplifier 10 may be performed bymore, fewer, or other components. As used in this document, “each”refers to each member of a set or each member of a subset of a set.

FIG. 2 is a circuit diagram of an example power amplifier 100 of theembodiment of FIG. 1. Power amplifier 100 includes driver stages 120,124, and 128. Driver stage 120 includes transistor 140, driver stage 124includes transistor 144, and driver stage 128 includes transistor 148.Driver stages 120 and 124 are coupled by a current sharing coupling 130.

TABLES 1, 2, and 3 provide example values for the components of poweramplifier 100. The values provided are examples only. The values ofother example power amplifiers may be different from the valuespresented in the TABLES 1, 2, and 3.

TABLE 1 presents example values for the capacitors of power amplifier100.

TABLE 1 Capacitor Capacitance (pF) C1 1.50 C2 14.90 C3 24.80 C4 13.00 C57.00 C6 6.04 C7 0.70 C8 3.00 C9 0.35 C10 6.04 C11 0.95 C12 0.31 C13 0.31C14 1.20 C15 14.90 C16 24.80 C17 2.00

TABLE 2 presents example values for the transistors of power amplifier100.

TABLE 2 Transistor Type Size (μm) Q1 5 × 40 200 Q2 5 × 40 200 Q3 5 × 40550 Q4 (switch) 1 × 35 35 Q5 (switch) 1 × 100 100

TABLES 3 presents example values for the resistors of power amplifier100.

TABLE 3 Type: Tantalum (T) Resistance Resistor Mesa (M) (Ω-mm) R1 42 ×10.5 (T) 24.0 R2 90 × 9.90 (T) 60.0 R3 16 × 6.5 (T) 15.0 R4 16 × 9.6 (T)10.0 R5 30 × 18.0 (T) 10.0 R6 20 × 6.7 (T) 18.0 RG1 42 × 29.0 (M) 275.0RG2 42 × 39.9 (M) 200.0 RG3 42 × 53.2 (M) 150.0 RG4 10 × 28.4 (M) 75.0RG5 22 × 50.9 (M) 85.0 RG6 22 × 54.1 (M) 80.0 RG7 22 × 57.7 (M) 75.0 RG820 × 22.7 (M) 174.0 RG9 14 × 26.0 (M) 110.0 RG10 14 × 24.9 (M) 115.0RG11 14 × 22.9 (M) 125.0 RG12 101 × 7.0 (T) 86.0 RG13 14 × 28.6 (M)100.0 RG14 14 × 26.0 (M) 110.0 RG15 14 × 24.9 (M) 115.0 RG16 50 × 13.5(M) 698.1 RD1 90 × 17.5 (M) 960.0 RD2 26 × 14.9 (M) 340.0 RD3 26 × 15.8(M) 320.0 RD4 26 × 16.9 (M) 300.0 RD5 26 × 20.2 (M) 250.0 RD6 26 × 15.8(M) 320.0 RD7 26 × 14.9 (M) 340.0 RD8 100 × 18.6 (M) 1000.0 RD9 250 ×26.4 (M) 1742.0 RD10 600 × 21.2 (M) 600.0 RD11 760 × 13.4 (M) 10394.0

According to one embodiment of the invention, voltage applied totransistors 140 and 144 of driver stages 120 and 124, respectively, maybe scaled to control power consumption by driver stages 120 and 124. Thescaling may improve the power added efficiency of power amplifier 100.

Modifications, additions, or omissions may be made to amplifier 100without departing from the scope of the invention. The components ofamplifier 100 may be integrated or separated according to particularneeds. Moreover, the operations of amplifier 100 may be performed bymore, fewer, or other components.

FIG. 3 is a graph illustrating the driver performance over voltage of anexample power amplifier of the embodiment of FIG. 1. The example poweramplifier may be operating at room temperature with an input power of 0dBm. According to the graph, a greater than 44% band average addedefficiency may be achieved over an output power range of approximately19 to 25 dBm.

Modifications, additions, or omissions may be made to the graph withoutdeparting from the scope of the invention.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that currentmay be shared between driver stages of a power amplifier. The outputpower of each stage may be scaled to control power consumption by thedriver stages. The output power scaling may improve the power addedefficiency of the power amplifier.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.Accordingly, the above description of example embodiments does notconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. A power amplifier for amplifying a signal, comprising: a plurality ofamplifier stages of the power amplifier, an amplifier stage operable toprocess the signal received by the power amplifier, an amplifier stagecomprising a transistor, at least one amplifier stage comprising adriver stage operable to supply excitation to a next stage to amplifythe signal, the plurality of amplifier stages comprising: a firstamplifier stage having a first transistor, the first amplifier stageassociated with a first output power; and a second amplifier stagehaving a second transistor, the second amplifier stage associated with asecond output power and operable to operate under compression; and acurrent sharing coupling operable to couple the first amplifier stageand the second amplifier stage, the first amplifier stage and the secondamplifier stage sharing a current through the current sharing coupling,the current sharing coupling operable to facilitate scaling of the firstoutput power and the second output power.
 2. The power amplifier ofclaim 1, further comprising: a voltage source operable to apply voltageto the first transistor and the second transistor to facilitate scalingof the first output power and the second output power.
 3. The poweramplifier of claim 1, wherein: the first transistor has a first size;and the second transistor has a second size, the first size and thesecond size selected to facilitate scaling of the first output power andthe second output power.
 4. The power amplifier of claim 1, wherein: thefirst amplifier stage has a first resistance; and the second amplifierstage comprises a second load target having a second resistance, thefirst resistance and the second resistance selected to facilitatescaling of the first output power and the second output power.
 5. Amethod for amplifying a signal, comprising: receiving the signal at aplurality of amplifier stages of a power amplifier, an amplifier stageoperable to process the signal, an amplifier stage comprising atransistor, at least one amplifier stage comprising a driver stageoperable to supply excitation to a next stage to amplify the signal, theplurality of amplifier stages comprising: a first amplifier stage havinga first transistor, the first amplifier stage associated with a firstoutput power; and a second amplifier stage having a second transistor,the second amplifier stage associated with a second output power;coupling the first amplifier stage and the second amplifier stage with acurrent sharing coupling; operating the second amplifier stage undercompression; and sharing a current between the first amplifier stage andthe second amplifier stage through the current sharing coupling, thecurrent sharing coupling operable to facilitate scaling of the firstoutput power and the second output power.
 6. The method of claim 5,further comprising: applying voltage to the first transistor and thesecond transistor to facilitate scaling of the first output power andthe second output power.
 7. The method of claim 5, wherein: the firsttransistor has a first size; and the second transistor has a secondsize, the first size and the second size selected to facilitate scalingof the first output power and the second output power.
 8. The method ofclaim 5, wherein: the first amplifier stage has a first resistance; andthe second amplifier stage comprises a second load target having asecond resistance, the first resistance and the second resistanceselected to facilitate scaling of the first output power and the secondoutput power.
 9. A power amplifier for amplifying a signal, comprising:a plurality of amplifier stages of the power amplifier, an amplifierstage operable to process the signal received by the power amplifier, anamplifier stage comprising a transistor, at least one amplifier stagecomprising a driver stage operable to supply excitation to a next stageto amplify the signal, the plurality of amplifier stages comprising: afirst amplifier stage having a first transistor, the first amplifierstage associated with a first output power; a second amplifier stagehaving a second transistor, the second amplifier stage associated with asecond output power and operable to operate under compression; and athird amplifier stage having a third transistor, the third amplifierstage associated with a third output power; and a current sharingcoupling operable to couple the first amplifier stage and the secondamplifier stage, the first amplifier stage and the second amplifierstage sharing a current through the current sharing coupling, thecurrent sharing coupling operable to facilitate scaling of the firstoutput power and the second output power.
 10. The power amplifier ofclaim 9, further comprising: a voltage source operable to apply voltageto the first transistor and the second transistor to facilitate scalingof the first output power and the second output power.
 11. The poweramplifier of claim 9, wherein: the first transistor has a first size;and the second transistor has a second size, the first size and thesecond size selected to facilitate scaling of the first output power andthe second output power.
 12. The power amplifier of claim 9, wherein:the first amplifier stage has a first resistance; and the secondamplifier stage comprises a second load target having a secondresistance, the first resistance and the second resistance selected tofacilitate scaling of the first output power and the second outputpower.
 13. A system for amplifying a signal, comprising: means forreceiving the signal at a plurality of amplifier stages of a poweramplifier, an amplifier stage operable to process the signal, anamplifier stage comprising a transistor, at least one amplifier stagecomprising a driver stage operable to supply excitation to a next stageto amplify the signal, the plurality of amplifier stages comprising: afirst amplifier stage having a first transistor, the first amplifierstage associated with a first output power; and a second amplifier stagehaving a second transistor, the second amplifier stage associated with asecond output power and operable to operate under compression; means forcoupling the first amplifier stage and the second amplifier stage with acurrent sharing coupling; and means for sharing a current between thefirst amplifier stage and the second amplifier stage through the currentsharing coupling, the current sharing coupling operable to facilitatescaling of the first output power and the second output power.
 14. Apower amplifier for amplifying a signal, comprising: a plurality ofamplifier stages of the power amplifier, an amplifier stage operable toprocess the signal received by the power amplifier, an amplifier stagecomprising a transistor, at least one amplifier stage comprising adriver stage operable to supply excitation to a next stage to amplifythe signal, the plurality of amplifier stages comprising: a firstamplifier stage having a first transistor, the first amplifier stageassociated with a first output power, the first transistor having afirst size, the first amplifier stage comprising a first load targethaving a first resistance; and a second amplifier stage having a secondtransistor, the second amplifier stage associated with a second outputpower, the second transistor having a second size, the first size andthe second size selected to facilitate scaling of the first output powerand the second output power, the second amplifier stage comprising asecond load target having a second resistance, the first resistance andthe second resistance selected to facilitate scaling of the first outputpower and the second output power, the second amplifier stage operableto operate under compression; a current sharing coupling operable tocouple the first amplifier stage and the second amplifier stage, thefirst amplifier stage and the second amplifier stage sharing a currentthrough the current sharing coupling, the current sharing couplingoperable to facilitate scaling of the first output power and the secondoutput power; and a voltage source operable to apply voltage to thefirst transistor and the second transistor to facilitate scaling of thefirst output power and the second output power.